Y-Cut Bulk Acoustic Sensor With Floating Electrode for Liquid Sensing
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Solution Overview
Problem
Current film bulk acoustic resonators face challenges in liquid sensing due to high acoustic losses and require electric contacts on both sides of the piezoelectric membrane, limiting their usability in liquid environments.
Innovation Solution
The development of a Y-cut film bulk acoustic resonator (YBAR) with a piezoelectric plate attached to a substrate, featuring a floating back-side conductor pattern and a sensing layer, which allows for shear mode operation without electric fields in the sample medium, enabling high sensitivity and robustness in liquid environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If extension mode vibrations are used in FBARs for liquid sensing, then the resonator can operate at higher frequencies, but the liquid load introduces unacceptable high acoustic losses
Solution Approach 1:
The patent changes the vibration mode parameter from extension mode to shear mode, and changes the cut orientation parameter to Y-cut, which fundamentally alters how the resonator interacts with the liquid load, enabling high-frequency operation with reduced acoustic losses
2Reliability
If electric contacts are placed on both sides of the piezoelectric membrane in FBARs, then the resonator can function properly, but this requirement limits usability in liquid environments
Solution Approach 1:
The patent extracts the back-side electrode from the liquid-exposed environment and places it on the opposite side of the piezoelectric membrane from the liquid contact surface, eliminating the problem of liquid degradation while maintaining proper resonator function
3Measurement precision
If Lamb wave sensors exploiting S0 mode are used, then the sensor can detect target species, but the sensor suffers from increased loss when submerged in liquid or having liquid deposited on one side
Solution Approach 1:
The patent changes the wave mode parameter from S0 Lamb wave mode to shear horizontal mode, and changes the cut orientation to Y-cut, which fundamentally alters the acoustic field distribution and eliminates the increased loss problem when liquid is present
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The YBAR sensor achieves high sensitivity and robustness in liquid environments with minimal acoustic energy transfer to the sample medium, allowing uninterrupted flow and precise detection of target species, with frequency shifts measurable even for single molecular layers.
Implementation Method 1
a piezoelectric plate attached to a substrate
Implementation Method 2
The presence of the captured species causes a measurable shift in the resonance frequency of the acoustic wave resonator
Implementation Method 3
an acoustic wave resonator may be coated with a sensing material capable of absorbing, adsorbing, or otherwise capturing the material or species to be detected
Data Source
AI summary
Acoustic sensor devices and sensor systems are disclosed. An acoustic sensor device includes a piezoelectric plate having a front surface and a back surface. A floating back-side conductor pattern is formed on the back surface. A first and second front-side conductor patterns are formed on a portion of the front surface opposite the back-side conductor pattern. A sensing layer is formed over all or a portion of the floating back-side conductor pattern.